The present invention relates generally to oilfield operations, and more particularly, to methods and systems for determining anisotropy, dip, and azimuth from image data.
When performing oilfield operations it is important to understand the structure and properties of the formation surrounding the well. The geological properties of the formation are important throughout the development of a well. For example, the geological properties of the formation can be used to determine if the formation contains hydrocarbons, determine the producibility of the hydrocarbons in the formation, and optimize production from the well.
Wireline logging and/or logging-while-drilling (LWD) or measurement-while-drilling (MWD) (collectively “logs”) are commonly used to obtain measurements that shed light on the geological properties of a formation. Accordingly, one or more logging tools may be lowered into the borehole and used to obtain measurements as the tools traverse the borehole. These measurements may then be used to estimate a number of desired formation properties.
One popular logging method utilizes nuclear magnetic resonance (“NMR”) measurements. The NMR measurements are based on the fact that when an assembly of magnetic moments, such as those of hydrogen nuclei, are exposed to a static magnetic field, they tend to align along the direction of the magnetic field, resulting in bulk magnetization. Accordingly, the magnetic properties of the nuclei may be used to obtain information about formation properties. Because of its non-destructive character, NMR logging has become one of the common methods for formation evaluation. NMR logging devices may be used independent of the drilling apparatus (i.e. in wireline logging) or in conjunction with the drilling apparatus (i.e. LWD/MWD) to obtain measurements while drilling is taking place.
One of the applications of NMR and other logging techniques is the analysis of certain properties of the geological formation. Such properties may include, for example, permeability, porosity, resistivity, diffusivity, or viscosity. Anisotropic analysis of properties is particularly useful in reservoir engineering where data or logs obtained through multiple measurements at different locations may be combined in order to characterize each flow interval of the geological area by a single anisotropy, such as permeability anisotropy. The process of combining the data obtained through multiple measurements and multiple locations is referred to as “up-scaling”. Because the measurement data are typically taken at various scales and use different sample sizes, up-scaling the data can be difficult.
Typically, the measurement data is processed by visual inspection and/or correlation. For instance, a single anisotropy, such as permeability anisotropy obtained for a flow interval, may be used to predict the producibility of the well. It is often necessary to perform well testing before such performance predictions can be made. However, the performance of well testing has become undesirable due to the high economic and environmental costs associated with it.
Additionally it is desirable to obtain dip information for a geological formation. The sedimentary portion of the earth's surface is made up of successive layers or beds which do not typically have a constant thickness. These layers often exhibit a certain dip, e.g., an inclination with respect to a horizontal plane. The dip angle is the angle between the vertical direction and a line perpendicular to the bedding plane. The relative borehole dip is the angle between the borehole and a line perpendicular to the bedding planes. The dip of formation layers in a formation penetrated by a borehole may convey important information in petroleum prospecting. For example, such information may be useful for evaluating the chances of obtaining hydrocarbons from a borehole, for establishing the nature of adjacent geological structures and for choosing the location of new boreholes.
Accordingly, it is desirable to develop an up-scaling method which honors the petrophysical spatial relationships of the data and can be used to combine different types of data including core data, wireline logs, wireline tester data and well testing to obtain image data anisotropy and the dip angle of the anisotropy. The azimuth angle is associated with the dipping plane and is the angle formed by the plane defining the anisotropy with respect to the north axis of the earth. Relative azimuth is the angle formed by the anisotropy plane and its intersection to the borehole.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.